"This is incredibly precious and rare wetland environment that a dying, ailing government in the shadow of an election is putting to the sword, it's not acceptable."

Greens MP Lynn Maclaren agreed.

"Now is the time to stand up against this process and I personally want to thank those people who have taken that extraordinary step forward and no doubt there will be many more before this is over," she said.

"It has been an incredible show of compassionate defence for the wetlands."

The High Court is expected to deliver a decision in the coming days on whether environmental approvals given to the project can be challenged.

The protesters, including Aboriginal Elder Ben Taylor, want all work to stop until then.

"They're going to disturb all the wetlands. For thousands of years Aboriginal people have taken care of that, to bulldoze this now is like killing he heart of our mother," Mr Taylor said.

"It's very sad that we've been given up like this."

The Government says the Roe 8 extension will take 2,000 trucks off Leach Highway each day, between the freeway and Stirling Highway, and thousands more off surrounding roads.

The project proved controversial for economic and environmental reasons, with critics arguing it will cause irreversible damage to the wetlands and Labor calling for it to be halted ahead of the state election.

Opponents are also seeking leave to appeal to the High Court against the environmental approval of Roe 8.